Biological Hydroxyapatite Research Articles

Sintered porous DP-bioactive glass and hydroxyapatite as bone substitute

There is extensive experimental and surgical experience with the use of bone tissue to fill defects in the skeleton, to bridge non-union sites, and to pack defects in bone created from cyst curettage. DP-bioactive glass with a chemical composition of Na 2O 8.4%, SiO 2 39.6%, P 20 5 12% and CaO 40% has been reported as an alternative bone substitute of high mechanical strength, good biocompatibility and which has a tight bond with living tissue. The bonding layer between DP-bioactive glass and bone tissue was considered to be formed by dissolution of calcium and phosphate ions from the DP-bioactive glass into the surrounding body fluids. The biological hydroxyapatite was suspected to deposit directly onto the bonding layer. In order to confirm the interaction between the DP-bioactive glass and bone tissue, the developed bioactive glass was implanted into rabbit femur condyle for 2–32 weeks. The histological evaluation of DP-bioactive glass as a bone substitute was also investigated in the study. Porous hydroxyapatite bioceramic was used in the control group and the results were compared with those of DP-bioactive glass. The interface between the DP-bioactive glass and bone tissue examined with SEM-EPMA showed that the bioactive glass formed a reaction layer on the surface within 2 weeks after operation and formed a direct bond with natural bone. The elements contained in the bioactive glass apparently interdiffuse with the living bone and biological hydroxyapatite deposited onto the diffusion area, which was proved by EPMA and TEM. After implantation for over 8 weeks, the DP-bioactive glass was gradually biodegraded and absorbed by the living bone. Histological examination using the optical microscope showed that osteocytes grow into the inside of the DP-bioactive glass and the bioactive glass would be expected to be a part of bone. Biomaterials (1994) 15, (13) 1087–1098

Bioactive Glass Templates for the Synthesis of Bone-Like TissueIn Vitro

AbstractPorous glass templates of pore size 75–200 14m and 20–30% porosity were synthesized. The glass disks were conditioned in a modified tris buffer (SBF) for 48 hrs and then treated with tissue culture medium (TCM) for 1 hr at 37°C. Other porous glass templates were treated with either SBF or TCM. The conditioned glass disks were seeded with 106neonatal rat calvaria osteoblasts and maintained in culture for 2, 5 or 7 days. It was found that the bioactive glass was rapidly invaded by cells which colonized the porous template. Morphological and biochemical analyses suggested that a bone-like tissue was formed inside templates conditioned with both SBF and TCM. By 7 days, the cells exhibited high alkaline phosphatase activity and synthesized osteocalcin. SDS-PAGE indicated the presence of type I collagen. SEM-EDAX analysis showed the formation of a bone-like tissue throughout the entire sample, while inspection of the Ca:P ratio indicated that the cells synthesized a mineral phase. Indeed, the FTIR spectra of the mineral confirmed that it was a biological hydroxyapatite. The rapid formation of the bone-like material within the templatein vitrosuggests that this template may be valuable clinically for the repair of bone lesions.

燐酸オクタカルシウム（ＯＣＰ）による歯槽堤増大に関する実験的研究

Progressive resorption of the alveolar ridge after tooth extraction results in diminished retention and stability of a denture. Preprosthetic augumentation of the alveolar ridge is therefore required to provide a firm base for a denture and reconstruct the functional occlusion in the field of oral and maxillofacial surgery.Octacalcium phosphate (OCP), the putative precursor of biological hydroxyapatite, was implanted into the subperiosteal pocket adjacent to the mandibular alveolar ridge in 7-week-old male Wistar rats. Soft radiographic and the histological examinations were performed to investigate the biological response to the OCP implant and assess possibilities for the clinical application.OCP was prepared using the method of LeGeros; granules between 32 and 48 mesh were used for implantation. Four rats were used in each experimental group. The animals were perfused with 4% paraformaldehyde in 0.1 M phosphate buffer at pH 7.4. After soft radiographic examination, the specimens were decalcified in a mixed solution of sodium citrate and formic acid, embedded in paraffin, sliced into thin sections, and stained with hematoxylin and eosin.In the experimental group, signs of radiopacity were not obvious at the implantation site at one week. At two weeks, increased signs of radiopacity were noted at the implantation site. The radiopacity increased markedly by four weeks after implantation and seemed to be relatively homogeneous, well amalgamated to the contiguous bone. Bone resorption was not obvious at the implantation site after eight weeks.Histologically, the implanted-OCP (i-OCP) was stained by hematoxylin at one week. The ridge was augumented at the region corresponding to the implantation site. Numerous connective tissue cells and inflammatory cells were surrounding i-OCP. Additional bone formation increased with time. I-OCP tended to aggregate and be resorbed. Two weeks after implantation, inflammatory cells decreased. After four weeks, i-OCP was surrounded by new bone. The newly formed bone was observed to mature with time and was not resorbed after eight weeks. The present study suggested that OCP is a useful material to augument the atrophic alveolar ridge in preprosthetic surgery.

Preferential adsorption of dentin and bone acidic proteins on the (100) face of hydroxyapatite crystals

Interaction of bone and dentin proteins with minerals is an elementary step in the regulation of mineralization in these tissues. Adsorption of acidic non-collagenous proteins on hydroxyapatite was examined using fluorescence-labeled protein and synthetic hydroxyapatite. Phosphophoryn, bone Gla protein, osteonectin and bone small proteoglycan II were prepared and labeled with fluorescein. All of these proteins were adsorbed on hydroxyapatite with a dissociation constant on the order of 10 −7 M. The more acidic proteins had lesser binding capacities. Hydroxyapatite single crystals were incubated with labeled proteins and observed with a fluorescence microscope. Phosphophoryn and other acidic proteins were adsorbed preferentially on the (100) face of the crystal. This preferential adsorption of the acidic proteins may be responsible for the morphogenesis of biological hydroxyapatite.

A Raman and infrared spectroscopic investigation of biological hydroxyapatite

Raman spectra were acquired on ox femur samples treated with hydrazine to remove the organic components of bone. A large increase in the signal-noise ratio of the mineral spectrum resulted from the exposure of the mineral surface and the removal of fluorescent components of the organic matrix. The effect of hydrazine treatment of the mineral matrix has been reinvestigated and shown to be slight on the basis of second derivative FTIR data. This is the first time that this high resolution technique has been applied to biological minerals.

Direct Structure Imaging In Hydroxyapatite

Human tooth enamel is composed 96% by weight of carbonated hydroxyapatite (HAP). It Js believed that the carbonate ions substitute for the phosphate ions in HAP, and it is expected that the carbonate will have an effect on the rate of dissolution of HAP during the carious process in human tooth enamel. In the present study high resolution electron microscope images of synthetic stoichiometric HAP were obtained to explore the possibility of obtaining direct structure images in HAP, and to provide a standard to which human enamel HAP could be compared. Bres et al have pointed out that structure images of HAP may provide a means of studying the substitution by carbonate of phosphate or other ions in biological HAP. The specimens were examined with a top-entry JEOL 4000EX HREM fitted with a Cs = 1.0mm objective pole-piece at 400kV. This 4000EX has demonstrated a structure resolution limit of better than 1.8 Å.

Mineralization of invertebrate cartilage.

Although invertebrate cartilage tissues do not mineralize in nature, it is now reported for the first time that when excised gill cartilage tissue from Limulus (horse shoe crab) is placed in an appropriate incubation medium metastable to hydroxyapatite, mineralization will occur. The mineralization is temperature dependent, and takes place at 37 degrees but not at 20 degrees. Incubations in media metastable to calcite have not produced mineralization. Histologic examination of mineralized tissues showed mineral deposits predominantly within cells, and to a lesser extent in the matrix. X-ray diffraction of the deposited mineral revealed a typical biological hydroxyapatite pattern.

A MO‐SCF study of hydroxyl binding and hydroxyl diffusion in pure and fluorine‐containing hydroxyapatite

AbstractHydroxyl diffusion and interhydroxyl binding in hydroxyapatite has been studied. LCGO‐MO‐SCF calculations have been carried out on groups of hydroxyl ions in a perfect and a vacancy‐containing crystal.Electrostatic crystal effects were accounted for by including the crystal potential field in the SCF calculations. Nearest‐neighbour interactions were calculated to first order. Effects exerted by fluorine impurities were considered for the vacancy‐containing crystal.The calculations indicate that narrow bandwidths obtained in nmr experiments on biological hydroxyapatite may be caused by a hydroxyl displacement mechanism and that no interhydroxyl hydrogen bonds exist in hydroxyapatite. The suggestion that the caries‐inhibiting properties of fluorine impurities in human dental enamel is caused by a diffusion‐binding mechanism is supported by the results.